1. Field of the Invention
The present invention relates to a booster circuit, and a solid-state imaging device, typified by a CMOS image sensor, and a camera system to both of which the booster circuit is applicable.
2. Description of the Related Art
In recent years, a CMOS image sensor is drawing attention as a solid-state imaging device (image sensor) to replace a CCD (Charge Coupled Device).
This is because the CMOS image sensor overcomes the following problems.
A dedicated process is needed to fabricate CCD pixels, and a plurality of supply voltages are needed for the operation of the CCD pixels. In addition, it is necessary to combine a plurality of peripheral ICs with the CCD pixels and operate the peripheral ICs.
The use of such a CCD raises various problems including one to make the system very complex, which are overcome by the CMOS image sensor.
The fabrication process for a general CMOS integrated circuit can be used in fabricating a CMOS image sensor. In addition, the CMOS image sensor can be driven by a single power supply. Further, an analog circuit and a logic circuit using the CMOS process can be mixed in the same chip.
The CMOS image sensor therefore has a plurality of significant merits including one capable of reducing the number of peripheral ICs.
The mainstream of the output circuit of a CCD is 1-channel (ch) output using an FD amplifier having an FD (Floating Diffusion).
By way of contrast, a CMOS image sensor has an FD amplifier for each pixel, the mainstream of the output of the CMOS image sensor is a column parallel output type which selects one row of pixels from a pixel array and reads out charges from the pixels in the column direction at a time.
This is because the FD amplifier disposed in a pixel has a difficulty in obtaining sufficient drive performance, thus making it necessary to lower the data rate, so that parallel processing is advantageous.
Such a CMOS image sensor with a sensor section includes a pixel array section having a two-dimensional array of pixel circuits having a predetermined structure, a pixel drive section (vertical scanning circuit), and a column circuit (column processing circuit).
Those sections are formed in large-scale integration (LSI).
From the viewpoint of providing an LSI with a single power supply, it is useful to provide a circuit for boosting or stepping down an externally supplied voltage inside the LSI.
For example, a CMOS image sensor often uses two kinds of supply voltages supplied externally, namely a voltage for analog circuits and a voltage for digital circuits.
In making the use of the merit of the CMOS image sensor that the CMOS image sensor can be fabricated in the same process as used for a general-purpose CMOS LSI, providing a step-up/step-down circuit in the sensor can allow multiple types of supply voltages to be used in the circuits in the image sensor.
That is, although only two kinds of voltages are supplied externally, the circuits inside the CMOS image sensor can operate as an aggregate of multi power supply circuits. (See Japanese Patent No. 3802239 (Patent Document 1)).